The invention relates to a device for the low-deformation support of an optical element, in particular of an end plate of a lens in a projection printing system for semiconductor elements, according to the type defined in more detail in the preamble of claim 1. The invention also relates to a method for the low-deformation support of the optical element.
A device of the generic type is described in DE 41 13 956 C2. Accordingly, it is already known to provide a bonding layer solely in the circumferential region between an optical element and a mount surrounding it. Furthermore, the mount is provided with a groove which prevents adhesive from migrating beyond the actual adhesive contact surface, e.g. due to capillary actions. In addition to the adhesive bonding, which extends over the entire circumferential region, the optical element is held or clamped in place in the axial direction by a type of securing ring. The object of the previously known device is to produce a defined adhesive joint which can absorb the thermal differential expansions between mount and optical element.
Known end plates in lenses of a projection printing system have an L-shaped rotationally symmetrical bonding surface. Bonding cement is applied to this bonding surface. After the hardening, the bonding surface is turned out to form an L-shaped bonding cement bed, so that a uniform bearing surface is obtained. Bonding cement is again applied to this bearing surface and then the end plate is pressed in. The bonding cement finally hardens and the residues are removed.
However, a disadvantage with this bonding method known from practice is that distortion is induced in the end plate via moments due to the L-shaped bonding location. In addition, this manufacturing process involves considerable outlay, because, after the first application of a bonding layer, which is intended to ensure that there is equalization over the circumference, thus avoiding a situation in which the end plate still touches the metal of the mount somewhere or other, the bonding layer must then be left for a period until it has hardened, the device must be clamped in a tool, and the bearing surface must be turned out uniformly. only then is the actual bonding layer applied to the L-shaped bonding surface.
During the application of the bonding layer, it has now also been found that distortions varying with respect to time occur between the optical element, in particular an end plate of a lens for a projection printing system. In this case, the distortions vary during the hardening of the bonding layer, even when the end plate is cleaned.
The object of the present invention is to provide a device of the type mentioned at the beginning in which the optical element is at least largely free of deformations or can be supported in the mount while avoiding distortions, in particular to provide a support by means of which the distortions varying with respect to time are at least largely eliminated.
According to the invention, this object is achieved by the features mentioned in the defining part of claim 1. A method according to the invention for the low-deformation support is specified in claim 7.
According to the invention, freedom from distortions is at least largely achieved by adhesive bonding only at the lateral surface or the adjacent circumferential walls of mount and optical element. In order to prevent the optical element from being pushed through and in order to achieve more accurate positioning of the optical element, at least three bearing feet on which the plate rests directly are attached to the mount. Defined three-point bearing is achieved in this way.
Adhesive webs, by means of which the optical element is centered before the bonding layer is applied in the circumferential region, may advantageously be applied to the circumferential wall of the mount in the region of the bearing feet.
When, after the cement bed formed by the adhesive webs has hardened and been turned out, the bonding layer is subsequently placed over the entire circumferential region of the annular gap formed between the adjacent circumferential walls of mount and optical element, a seal is then also created at the same time between the mount and the optical element.
In a further, very advantageous refinement of the invention, provision may be made for the bearing feet to be provided with adhesive-receiving pockets.
The adhesive-receiving pockets form a gap, for which purpose they are preferably formed by radial recesses in the mount between the inner circumferential wall of the mount and the bearing feet. Adhesive from the adhesive webs can run into this gap. In this way, an escape space is provided for adhesive if too much adhesive is placed.